This invention relates to filters, and more particularly to a disposable filter cartridge which is disposable in an environmentally acceptable manner.
In our prior application, Ser. No. 08/575,833 (hereinafter our prior application), we disclosed and claimed a filter cartridge which proved to be a highly effective advance in the art. This application is intended to describe and claim certain improvements therein, particularly in the area of the end caps.
A very common use for such filters is in the lubrication system of the standard internal combustion engine, e.g., automotive engines, truck or heavy equipment engines, and stationary power sources. The invention, however, has broader applicability, and can also be used in hydraulic, fuel and air filter applications.
In all of these applications, the filter must be changed periodically. Taking the lubrication system example, man automotive application, the oil filter is typically changed every several thousand miles. There are a limited number of reusable oil filter types available or in use, but in most high quality lubrication systems, disposable spin-on oil filters are used, and these can create a disposal problem.
In the early days of filters, it had been common to utilize cartridge type oil filters which fit into a removable housing. The housing was removed from the oil filter mount on the engine, the cartridge removed from the housing, the housing cleaned, a new cartridge installed, and the housing with new cartridge then replaced on the engine. Cartridges for filters of that type usually included a cellulosic filtering medium and a supporting center tube, typically of metal mesh or expanded metal. Oftentimes, such cartridges also included an exterior metal support. The metal supports, and particularly the center tube (or outerwrap), were needed to prevent the filter from being crushed by the pressure generated in the lubricant being filtered.
Differential oil pressures in an automotive hydraulic system can rise substantially at engine start-up, and particularly during malfunctions such as a plugged filter malfunction (due, for example, to water or excess engine wear metals in the oil), and can reach 200 psi or more.
In summary, conventional practice in the past required the use of a support tube in combination with cellulosic filters. The cellulosic filter provided good filtering capability, and the metallic supporting structure,provided the necessary rigidity and differential pressure withstanding capability. Disposal of the cartridge was, complicated by the metal supporting structure which made crushing impractical and complete incineration impossible.
More modern automobiles have migrated to the spin-on filter. While the spin-on filter is typically more expensive, and creates a greater disposal problem, the simplicity of removing an old filter, then spinning a new one on in its place has driven the industry in that direction. The spin-on filter not only has the typical cellulosic filter elements, but also has an external shell of sheet metal, a center supporting tube, a threaded base plate and all the necessary structure to old the filter in place and keep it from being crushed. After it is used, the entire spin-on filter, metal shell and all, must be discarded.
Environmental regulations, the limited availability of landfills, and the greater awareness on the part of the public with respect to landfill pollution have created the need for an oil filter of the type which can be safely disposed of in an environmentally acceptable way. Certainly the canister type spin-on filters have their difficulty on this issue, because they have a substantial metal content, along with the paper content, gasket content, and residual oil. Even the older variety of cartridge type filters have disposal problems, because they contain both metallic parts (for support) as well as the cellulosic parts (for filtering).
Attempts have been made to produce an environmentally disposably acceptable filter (i.e., an environmentaly friendly filter), but they have also suffered their drawbacks. For example, it has been, proposed to utilize a filter cartridge with no metallic center support tube, and build the support tube into the filter housing. However, these approaches have been less than satisfactory for a number of reasons.
One of the problems is encountered when using a radial seal of the main seal between the inside of the filter and the atmosphere. The problem is the difficulty of disassembling the filter housing in order to change the cartridge. The sealing arrangements have been such that an unusual amount of torque is needed to detach the cover from the housing. Even more significantly, while the center support tubes have provided protection from crushing the filter paper elements in the radial direction, there are significant pressure drops experienced along the axis of the filter. Those pressure drops can be large enough to either unseat the filter and cause leakage around the gasket at one or the other end cap, or to begin to compress or crush the filter along its axis. Thus, in these attempts, while they apparently have provided a filter cartridge with no metallic parts, the filters themselves have been less desirable than standard types because of these difficulties.
It is possible, by making certain compromises, to compensate for the lack of strength of an unsupported filter cartridge by using bypass valves either in the filter or in the engine. The function of a bypass valve is to respond to a pressure differential buildup caused, for example, by a plugged filter, and bypass oil around the filter. In effect, the bypass valve limits pressures in the system, but at the cost of passing unfiltered oil to the equipment. That might be acceptable in an automotive application, but in other applications it is completely undesirable. For example, a pressure relief valve is undesirable in those cases where passing unfiltered fluid might do permanent damage to the machinery being protected. Typical examples are a diesel fuel system or a hydraulic system. In those, it is considered preferable to allow the filter to plug to protect the equipment from a catastrophic and costly failure. To withstand the pressures as the filter plugs in such systems, the filter cartridge must have adequate structural support, which eliminates the possibility of using the unsupported filter cartridges which have been available in the past.
In view of the foregoing, it is a general aim of the present invention to provide a filter cartridge which is crushable or burnable for disposal purposes, but which has operating characteristics capable of reliably meeting the stringent requirements normally associated with metal housed spin-on filters. Further in that regard, an object is to provide such a filter cartridge which does not require the use of a relief valve to limit pressure in the system. The invention can be used in relief valve systems, but the relief valve is not necessary to protect the filter.
It is an object of the present invention to provide a high performance filter cartridge having no metallic supporting elements, and adapted to cooperate with a filter housing such that the compressive forces on the filter element are limited and are tolerable.
It is a further object to control pressures applied to the filter cartridge in such a way that any axial forces on the filter media primarily place the media in tension (where the filter media has significant strength) rather than in compression (where it has much less strength).
A resulting object is to impose loads on the filter cartridge which it is capable of withstanding, such as compressive loads radially where the filter element is supported, and axial tension loads which the filter is more capable of supporting than axial compressive loads.
It is a detailed object of the invention to provide such a filter cartridge in both single flow and dual flow types.
A further detailed object is to provide such a filter assembly which is not only environmentally acceptable, but which is user friendly. In that respect, it is an object to provide a filter cartridge which can be installed in only one way, and in a way which assures that the filter assembly will be properly gasketed when assembled. In other words, an object is to make changing of the filter substantially foolproof, so that untrained individuals can reliably perform a filter change.